Bottom Line:
LOOS1 is distantly related to plant expansins through the shared presence of a DPBB domain, however domain II found in plant expansins is absent.LOOS1 is a new type of protein with disrupting activity on cellulose.LOOS1 binds polysaccharides, and given its enhancing properties on the action of hydrolytic enzymes, LOOS1 represents a potential additive in the production of fermentable sugars from lignocellulose.

Background: Expansins and expansin-like proteins loosen cellulose microfibrils, possibly through the rupture of intramolecular hydrogen bonds. Together with the use of lignocellulolytic enzymes, these proteins are potential molecular tools to treat plant biomass to improve saccharification yields.

Results: Here we describe a new type of expansin-related fungal protein that we have called loosenin. Its corresponding gene, loos1, from the basidiomycete Bjerkandera adusta, was cloned and heterologously expressed in Saccharomyces cerevisiae. LOOS1 is distantly related to plant expansins through the shared presence of a DPBB domain, however domain II found in plant expansins is absent. LOOS1 binds tightly to cellulose and chitin, and we demonstrate that cotton fibers become susceptible to the action of a commercial cellulase following treatment with LOOS1. Natural fibers of Agave tequilana also become susceptible to hydrolysis by cellulases after loosenin treatment.

Conclusions: LOOS1 is a new type of protein with disrupting activity on cellulose. LOOS1 binds polysaccharides, and given its enhancing properties on the action of hydrolytic enzymes, LOOS1 represents a potential additive in the production of fermentable sugars from lignocellulose.

Mentions:
Loosenin disruptive-activity on cotton fibers was then investigated. Cotton fibers incubated for 8 h with 20 μg LOOS1, mock supernatant proteins or acetate buffer only were visualized by phase contrast microscopy. The cotton fibers in the untreated controls had a homogeneous structure with widths between 13 and 17 μm along the fiber (Figure 5). On the contrary, LOOS1-treated fibers showed local disruption of the fiber structure observed as enlarged "bubbles" (defined as those loosened structures measuring at least 40 μm width; Figure 5), 2.6 times wider with respect to the untreated controls. The occurrence of these bubbles also depended on the concentration of loosenin added, being observed at a frequency of 1 bubble/field at 20 μg (average width: 52.25 μm ± 10.07), and 1.6 bubbles/field at 40 μg (average width: 66.62 μm ± 10.62), compared to the absence of evident bubbles in the untreated control (which occasionally showed wider regions of up to 30 μm, average width: 26.60 μm ± 4.21) (Figure 5). Loosened areas of cellulose have been previously reported for fungal swollenins that show expansin-like activity [26].

Mentions:
Loosenin disruptive-activity on cotton fibers was then investigated. Cotton fibers incubated for 8 h with 20 μg LOOS1, mock supernatant proteins or acetate buffer only were visualized by phase contrast microscopy. The cotton fibers in the untreated controls had a homogeneous structure with widths between 13 and 17 μm along the fiber (Figure 5). On the contrary, LOOS1-treated fibers showed local disruption of the fiber structure observed as enlarged "bubbles" (defined as those loosened structures measuring at least 40 μm width; Figure 5), 2.6 times wider with respect to the untreated controls. The occurrence of these bubbles also depended on the concentration of loosenin added, being observed at a frequency of 1 bubble/field at 20 μg (average width: 52.25 μm ± 10.07), and 1.6 bubbles/field at 40 μg (average width: 66.62 μm ± 10.62), compared to the absence of evident bubbles in the untreated control (which occasionally showed wider regions of up to 30 μm, average width: 26.60 μm ± 4.21) (Figure 5). Loosened areas of cellulose have been previously reported for fungal swollenins that show expansin-like activity [26].

Bottom Line:
LOOS1 is distantly related to plant expansins through the shared presence of a DPBB domain, however domain II found in plant expansins is absent.LOOS1 is a new type of protein with disrupting activity on cellulose.LOOS1 binds polysaccharides, and given its enhancing properties on the action of hydrolytic enzymes, LOOS1 represents a potential additive in the production of fermentable sugars from lignocellulose.

Background: Expansins and expansin-like proteins loosen cellulose microfibrils, possibly through the rupture of intramolecular hydrogen bonds. Together with the use of lignocellulolytic enzymes, these proteins are potential molecular tools to treat plant biomass to improve saccharification yields.

Results: Here we describe a new type of expansin-related fungal protein that we have called loosenin. Its corresponding gene, loos1, from the basidiomycete Bjerkandera adusta, was cloned and heterologously expressed in Saccharomyces cerevisiae. LOOS1 is distantly related to plant expansins through the shared presence of a DPBB domain, however domain II found in plant expansins is absent. LOOS1 binds tightly to cellulose and chitin, and we demonstrate that cotton fibers become susceptible to the action of a commercial cellulase following treatment with LOOS1. Natural fibers of Agave tequilana also become susceptible to hydrolysis by cellulases after loosenin treatment.

Conclusions: LOOS1 is a new type of protein with disrupting activity on cellulose. LOOS1 binds polysaccharides, and given its enhancing properties on the action of hydrolytic enzymes, LOOS1 represents a potential additive in the production of fermentable sugars from lignocellulose.